One of the many difficulties in the area of biotechnology is to achieve a technically viable methodology for long term sustained delivery of proteins. This is often due to the observation that proteins can be easily hydrolyzed and denatured. Encapsulated proteins in resorbable polymeric microparticles for prolonged release has been extensively studied. The problem of configuring a sustained release of large molecules, e.g. an easily injectable means of administration is due to the high porosity of microparticles, resulting in two key issues that have not been fully resolved: 1) exposing the protein payload to its surrounding water resulting in hydrolysis, 2) the resultant acidity from polymer degradation causing denaturation.
Hypercompressed polymers and copolymers containing pharmaceuticals are known. However, when a high molecular weight peptide or a protein is made into a controlled release pharmaceutical the stability of peptides and proteins to hypercompression has not previously been determined.
A significant factor affecting the interaction between carrier polymers and the reactive species of degraded peptides and proteins is their proximity to each other. Since hypercompression positions the reactive species in closer proximity to one another, the hypercompression actually can facilitate further degradation which results in a less stable product with a shorter shelf life.
Current pharmaceutical regulations exist in the United States and in Europe that limit the amount of substances in pharmaceuticals which are related to the active pharmaceutical ingredient to no more than 1.0 wt % or 5 μg TDI (total daily intake) whichever is lower. for a maximum daily dose of 1.0 mg. These requirements pose a challenge to formulators of controlled release products.
It is known that certain peptides and recombinant proteins have a short biological half-life and low oral bioavailability which has forced pharmaceutical manufacturers to only provide injectable formulations which complicate the therapy for which these materials are indicated. This is of special concern when protein based pharmaceuticals are administered to the eye which sometimes requires frequent the intraocular injection of a protein which is unpleasant for the patient and also carries with it the risk of infections and other complications.
Formulations have been prepared where proteins have been combined with ester terminated poly(DL lactic-co-glycolic acid)(PLGA capped) as a technique for providing controlled release formulations of proteins that can be administered by implantation or other techniques that avoid the need for direct injection. The controlled release of these formulations, that were not subjected to hypercompression, is modulated by the selection of different size particles of the protein loaded PLGA particles and different weight ratios of lactic acid to glycolic acid. The use of smaller particles (0.3 μm) of PLGA protein loaded particles has been found to result in a slower release (in PBS, pH 7.4) of protein than the use of larger particles (1.0-20 μm) having the same composition. The use of both the smaller and larger particles of the PLGA capped-protein loaded particles result in a controlled release product that has a pronounced burst effect when it is tested for controlled release properties. In an attempt to increase sustained delivery for a period of time, physical/chemical modifications of the protein or dispersed in medium, (hydrogels) is made.
It has been found that if a composition of a protein dispersed in a PLGA polymer is densified by hypercompression, the burst effect (which may cause toxicity, or excessive waste of drug that compromises duration) seen in PLGA polymer formulations is attenuated or avoided. The reduction of the burst effect also results in a formulation that will deliver a therapeutic effect for a longer period of time than an uncompressed product.